It is conventional to provide both horizontal and vertical enhancement processes within a television system at the source. Typically, the signal is then encoded in a conventional signal format such as NTSC, PAL or Secam, RF modulated and transmitted (or recorded on magnetic tape), RF demodulated, decoded and displayed on a television display screen. Sometimes horizontal peaking is used at the display device.
This prior approach is illustrated in FIG. 1, labelled "Prior Art". Therein, a conventional television image system 10 includes a camera or other source 12 of video image information. A horizontal enhancement process 14 and a vertical enhancement process 16 cooperate with the source 12 to provide signal enhancement in the horizontal and vertical domains. An encoder 18 functions to encode chrominance and luminance components of the video image signal put out by the source 12 into signals following a predetermined signal format, such as NTSC, for example.
The output from the encoder 18 is then RF modulated and transmitted over a signal degrading medium, generalized by the block 20 of FIG. 1. Alternatively, the degrading path or medium may comprise playback of a video magnetic tape recording.
Following reception of the transmitted signal (or playback in the case of a video recording), the signal is decoded in a decoder 22 which functions to decode the format encoded by the encoder 18 (e.g. NTSC). A horizontal peaking process 24 may be included at the decoder 22. The decoder 22 typically puts out red, green and blue signals to a display device 26, such as a cathode ray tube, for example. This approach has been very useful for many years and has given the viewing public a very acceptable video image display quality.
However, this prior approach is no longer adequate for the developing needs of advanced television image systems, given the single channel limitations of transmission bandwidth (about 6 MHz in the NTSC signal format). Presently, it is most desirable to provide a picture resolution quality which is about twice that achieved by the conventional display devices (525 interlaced scan lines in the NTSC format). Such doubled virtual picture resolution is achievable by use of line doubling techniques, in combination with multiplicative horizontal transition enhancement techniques. Such techniques are described in the inventor's earlier U.S. Pat. No. 4,030,121 entitled "Video Crispener".
A hitherto unsolved need has therefore arisen for a reconfiguration of image enhancement processes within television systems including line doubling techniques for doubled virtual picture image resolution.